Among known outboard engine units are those including an air induction port disposed in the upper rear of the engine cover, an electrical box disposed in the upper front inside the engine cover, and an engine air intake port disposed in the vicinity of the electrical box (i.e., the upper front inside the engine cover). An example thereof is disclosed in Japanese Patent No. 4,005,198.
In the outboard engine unit disclosed in the above publication, air (from the exterior) is taken into the engine cover from the air induction port, and the air taken into the engine cover is directed to the electrical box via an upper space inside the engine cover. The air directed to the electrical box cools the electrical components inside the electrical box, and the air that has cooled the electrical components is taken into the throttle unit via the air intake port of the engine.
However, the outboard engine unit disclosed in Japanese Patent No. 4,005,198 has the air induction port, the electrical box, and/or the air intake port of the engine disposed in upper part of the engine cover. Therefore, the air taken into the engine cover from the air induction port is taken into the air intake port of the engine via the upper space inside the engine cover. In other words, it is difficult for the air taken in from the air induction port to circulate to the entire area inside the engine cover. Accordingly, there is a need to provide an arrangement that cools the entire area inside the engine cover with air taken into the engine cover from the air induction port, i.e., an arrangement that cools the entire engine with air.
Also known among outboard engine units is one having an air intake duct provided to the engine cover for covering the area above the engine, the inlet to the air intake duct opens to an air intake chamber, and the outlet of the air intake duct opens to an air induction pipe, as disclosed in Japanese Patent No. 3,608,637. The air intake chamber is in communication with the exterior of the engine cover via the air intake port of the engine cover. The air induction pipe is in communication with the throttle unit (throttle valve).
In the outboard engine unit disclosed in Japanese Patent No. 3,608,637, air is taken into the air intake chamber from the air intake port of the engine cover, and the air taken into the air intake chamber can be taken into the air intake duct from the inlet. The air taken into the air intake duct is taken into the air induction pipe via the outlet of the air intake duct, and the air taken into the air induction pipe is introduced to the throttle unit.
The outboard engine unit disclosed in Japanese Patent No. 3,608,637 has the air intake port of the engine cover disposed facing sideways when the outboard engine unit is mounted on a hull. Therefore, when air intake noise is generated in accompaniment with air intake pulsation or shockwaves when the engine is driven, the generated air intake noise is transmitted laterally from the air intake port of the engine cover via the air intake duct. Thus, air intake noise is transmitted laterally, whereby air intake noise can be made less likely to be transmitted to the hull side. However, it is difficult to sufficiently reduce air intake noise using a method that transmits air intake noise laterally.
Furthermore, in an outboard engine unit, ordinarily, the engine is covered by an engine cover, an opening for air intake is provided to the engine cover, and this opening is in communication with the throttle unit via the internal space of the engine cover. Among such outboard engine units are those provided with a silencer on the upstream side of the throttle unit so that air intake noise of the engine is reduced by the silencer. An example thereof is disclosed in Japanese Patent Application Laid-Open Publication No. 2002-235621.
When a silencer is provided to the outboard engine unit, the air directed to the internal space of the engine cover from the opening in the engine cover is directed to the silencer. The air directed to the silencer is taken into the throttle unit, and the air taken into the throttle unit is directed to the combustion chamber of the engine.
Ordinarily, in an outboard engine unit, it is known that air intake noise is generated in accompaniment with air intake pulsation or shockwaves when the engine is driven, and the generated air intake noise is transmitted to the exterior of the engine cover via the throttle unit or the like. In view of the above, the silencer is disposed upstream from the throttle unit, whereby air is made to expand in the silencer to reduce the air intake noise (i.e., sound pressure).
There are also outboard engine units configured so that the opening for air intake is in communication with the throttle unit via an intake channel inside the engine cover. In this air intake structure, the throttle unit (i.e., engine) is in direct communication with the opening for air intake via the intake channel. Accordingly, the air intake noise generated in accompaniment with air intake pulsation or shockwaves of the engine is readily transmitted to the exterior of the engine cover via the intake channel and the opening. For this reason, there is a need to develop a feature that further reduces the air intake noise generated in accompaniment with air intake pulsation or shockwaves of the engine.
In addition, in the case that the opening for air intake is placed in communication with the throttle unit via the intake channel, it is possible to consider directing water into the intake channel together with air when air is directed into the intake channel from the opening. For this reason, water directed into the intake channel tends to enter into the throttle unit via the intake channel, and there is a need to develop a feature that reduces the likelihood that water will enter into the throttle unit.